To reduce aircraft fuel burn, jet engines aim to maximize the bypass ratio. Maximizing the bypass ratio involves making fan flow as large as possible relative to the core engine flow. Increasing fan flow to maximize bypass ratio poses challenges when trying to minimize weight. If the fan becomes too heavy as a result of attempting to maximize the bypass ratio, this can lead to increased fuel consumption.
Using a lightweight material in the blade and restricting the use of a heavier, higher-strength material to only the sheath can help to keep weight down as engine bypass ratio is increased. A way of further reducing the weight of the material used for the blade is by including hollow cavities into the blade or by making it thinner. The sheath can give the blade much of the impact tolerance required to allow the engine to produce the required thrust after hitting medium-sized birds and to allow the engine to be safely shut down after hitting very large sized birds. This tolerance helps to protect against cracking, delamination, deformation and erosion. By decreasing the weight of blades, the weight of the disk spinning the blades and the weight of the containment system (in the case of a catastrophic failure) can also be reduced.